1. Field of the Invention
The present invention relates to the technology of fuses. More particularly, it relates to a flat fuse element—or strip—designed, especially, to react to overload currents of low magnitude but of long duration. The invention also relates to a method for the manufacture of such a fuse element.
2. Discussion of Related Art
To manufacture this type of fuse, it is known to deposit a small bead of a metal with a low melting point, such as tin, denoted by the expression “M-spot”, at the center of a silver ribbon which reacts in a conventional way to high overload currents (short circuits) but remains insensitive to low overload currents of long duration.
When a low overload current flows in the silver ribbon for a long period of time, its temperature increases progressively until it melts the small bead of tin. The alloying of the silver with the tin produces a eutectic having a much lower melting point than silver but with an electrical resistance high enough to cause the strip to meet at this point. Typically, this “M-spot” structure allows melting to take place at a temperature of 200 to 300° C., whereas the normal melting point of silver is 962° C.
Documents CH 587 559, U.S. Pat. No. 4,134,094 and GB 2 120 027, for example, describe structures of this type.